1. Field of the Invention
The subject invention relates generally to pre-filled syringes and to stoppers for such syringes.
2. Description of the Prior Art
The prior art syringe includes an elongate barrel having opposed proximal and distal ends and a fluid receiving chamber therebetween. The distal end of the prior art syringe barrel includes a small diameter passage that communicates with the fluid receiving chamber and with the lumen of a piercing element, such as a pointed needle cannula or a blunt-ended cannula, that is mounted to the syringe barrel. The proximal end of the prior art syringe barrel is generally open for slidably receiving a plunger. The plunger typically includes a distal end configured to mate with a rubber stopper that is in sliding fluid-tight engagement with the inner wall of the chamber. A distal force on the plunger and stopper urges fluid in the chamber through the passage of the syringe barrel and through the needle that communicates with the passage. A proximal force on the plunger and stopper urges fluid proximally through the passage and into the chamber of the prior art syringe barrel.
Many prior art syringes remain empty until shortly prior to use. These prior art syringes are used by placing the needle in communication with a drug and moving the plunger proximally to aspirate the drug into the chamber of the syringe barrel. The drug may then be administered by placing the distal end of the needle in communication with the patient or with an IV set or other device, and urging the plunger distally to expel the drug from the syringe barrel.
The filling of a syringe immediately prior to use requires the time, skill and attention of the health care worker. Health care workers often work under emergency circumstances with numerous simultaneous demands for their time, skill and attention. At the very least, filling a hypodermic syringe immediately prior to use creates an inconvenience for the healthcare worker, and can create the potential for improper selection and dosing of a drug.
Frictional forces between the rubber stopper and the syringe barrel can be significant and can impede a slow, predictable and accurate flow of drug into or out of the syringe barrel. As a result, most prior art syringes employ a low friction material or lubricant, oftentimes a silicone-based lubricant such as a silicone oil, to facilitate the sliding movement of the stopper in the syringe barrel. The lubricant may be applied as a coating over the stopper or may be applied to the walls of the chamber in the syringe barrel.
To avoid problems associated with filling the syringe immediately prior to use, pharmaceutical companies sometimes prefer to ship medicaments in pre-filled syringes. The pre-filled syringes are appropriately sealed, clearly labeled, and shipped to health care facilities in properly measured doses. Thus, a healthcare worker avoids many of the steps associated with point of injection syringe filling. The healthcare worker merely accesses an appropriate pre-filled syringe and injects the required dose without the above described inconveniences associated with filling the syringe immediately prior to use. Pre-filled syringes are widely used for a broad range of drugs that have an acceptably long shelf life. However, owing to certain factors such as the duration of storage which pre-filled syringes might sustain, many drugs that are otherwise appropriate for pre-filled syringes may sometimes be incompatible with the lubricant or low friction material, such as silicone oil, used to facilitate the sliding movement of the stopper through the syringe barrel. For instance, protein based drugs or drugs based on biogenetic technology may sometimes display compatibility difficulties respective of the silicone employed as a syringe lubricant.
The prior art includes stoppers with laminated films or coatings to reduce friction without using silicone-based lubricants. For example, U.S. Pat. No. 5,009,646 teaches laminating a rubber elastic body with a tetrafluoroethylene resin, an ethylenetetrafluoroethylene resin or a UHMW polyethylene resin. These laminated stoppers may work well for syringes that are filled immediately prior to use. However, the laminated materials may tend to creep after placement in the syringe barrel. As a result, microchannels are opened that may permit the drug in the syringe barrel to communicate with ambient air. Thus, the adequacy and effectiveness of the drug can be compromised by using these prior art stoppers laminated with a non-silicone, low friction material.
In view of these problems, certain drugs that would otherwise be appropriate for pre-filled syringes must be filled immediately prior to use by the health care worker to avoid contaminating the drug, either because of the presence of lubricants or low friction materials such as silicone-based lubricants or contamination owing to unwanted communication with the ambient atmosphere.